The script nix-install-package takes a `Nix package file' (which
  contains one or more derivations, along with URLs of Nix caches),
  unpacks it, pulls the caches, and installs the derivations in the
  user's environment.

  For best results, associate the command `xterm -e
  /nix/bin/nix-install-package' with the MIME type
  `application/x-nix-package' and visit
  http://losser.st-lab.cs.uu.nl/~eelco/test/.

* Hack: `nix-env -i *' installs all available derivations.

* More consistency checks.

  deleting a path in the store.
* Allow absolute paths in Nix expressions.
* Get nix-prefetch-url to work again.
* Various other fixes.

  configuration.
* Status queries.

* Replace all directory reading code by a generic readDirectory()
  function.

  that it can be used by multiple programs.

* Several bug fixes in the grammar.
* Allow one-line comments (#... and //...) to end in EOF.

* More refactoring.

* More refactoring.

* Add some rejections and lexical restrictions to the grammar to make
  this work. 

  turned out to be a huge performance bottleneck (the text to printed
  would always be evaluated, even when it was above the verbosity
  level).  This reduces fix-ng execution time by over 50%.

  gprof(1) is very useful. :-)